This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We study the pH dependent conformational switching of bromelain-released influenza hemagglutinin by small angle solution x-ray scattering. The trimeric hemagglutinin (HA) glycoprotein is responsible for both host cell attachment and membrane fusion in influenze virus. The acidic environment in endocytosis is known to trigger a large scale conformational switching. X-ray crystallography has given the three dimensional structures of the initial and the post fusion states. There is little structural information available so far for activated intermediate states due to their transient nature central to their host attachment and fusion functions. We trigger the conformational switching by lowering solution pH and monitor the evolution of HA conformation via solution x-ray scattering as a function of time over several minutes. We obtained encouraging results at BioCAT fairly similar to what we had obtained at SSRL in summer 2007. The improved data quality was evident at BioCAT. We observed x-ray scattering curves which has slightly different features at intermediary scattering angles than had been observed in 2007, indicating the slight variation in sample preparation. We are evaluating sample preparation protocol and planning on conducting additional experiments in near future.